Swimmer’s itch is caused by an allergic reaction to tiny parasite larvae in the water that can burrow into your skin while you’re swimming or wading, usually in freshwater lakes and ponds. The parasites come from infected birds or mammals, pass through snails, and then are released into the water; they cannot survive in people and die after entering the skin.

What happens

  • The larvae are released from infected snails into the water.
  • They mistake people for their normal hosts and try to burrow into the skin.
  • Your immune system reacts to them, which causes the itchy rash.

Common triggers

  • Warm, shallow, calm water.
  • Lakes and ponds with waterfowl or other animals that carry the parasite.
  • Staying wet and letting the water dry on your skin instead of toweling off.

Important note

Swimmer’s itch is not contagious from person to person. It’s usually uncomfortable but temporary, and the rash often clears within about a week.

Simple prevention

  • Towels off right after getting out of the water.
  • Avoid shallow, warm areas where the parasites are more likely to be present.
  • Shower as soon as possible after swimming.

If you want, I can also explain how to tell swimmer’s itch apart from a regular mosquito bite or lake rash.